It is known to apply paints of acrylic type to surfaces, in particular building façades, not only to embellish them and to prevent the deposition of dirt, in particular dust, but also in order to protect them against the infiltration of rainwater. To this end, the coating must be able to adhere suitably to the surface, deform easily without risk of cracking and not exhibit a tacky nature.
An example of a paint composition exhibiting the abovementioned compromise in properties has been disclosed in the application EP 0 599 676. This composition includes a polymer resulting from the polymerization of three distinct monomers, consisting in particular of a mixture of (meth)acrylic acid, a (meth)acrylic acid ester, such as n-butyl acrylate, and a benzophenone derivative, and optionally of a fourth monomer which is styrene.
Another type of paint composition has been described in the document US 2012/0121921. It is a flame-retardant and water-resistant polymer composition, comprising a polymer binder in the latex form, obtained by radical polymerization of at least one ethylenically unsaturated monomer, comprising in particular n-butyl acrylate, and of tert-butyl(meth)acrylate.
Acrylic compounds, optionally in combination with styrene, in addition exhibit the advantage of making possible the formulation of paints giving good resistance to light and to weather conditions. However, they are generally produced from propylene, which is a byproduct of the refining of oil. In point of fact, oil deposits are rapidly becoming exhausted. In order to anticipate the supplying difficulties relating to these resources, it would be desirable to be able to replace these acrylic compounds with compounds obtained from carbon sources of renewable origin.
In order to meet this need, provision has been made, in the application WO 2012/084974, to use, as binder in paints, a dispersion of two vinyl polymers including at least 10% by weight of monomers of renewable origin, such as n-butyl acrylate. It is indicated that this binder makes it possible to obtain a flexible and nontacky paint which dries at low temperature.
However, it is apparent to the applicant company that n-butyl acrylate does not include sufficient, carbon of renewable origin and that it exhibits a more hydrophilic nature than long-chain acrylates, such as 2-octyl acrylate.
After numerous research studies, the applicant company has demonstrated that it is possible to formulate a composition for coating in the film form, based on polymer of predominantly renewable origin, which composition simultaneously exhibits good mechanical properties, in particular a suitable flexibility and a suitable elongation and a good cohesion, and also a sufficiently hydrophobic nature, using, as binder, a homo- or copolymer based on 2-octyl acrylate.
Such a compound has already been described, in particular, in the application WO 2012/038441, as constituent of an impact modifier, and in the documents WO 2008/046000, WO 2009/079582, WO 2009/132098 and WO 2003/129087, as constituent of a pressure-sensitive adhesive.
In the document U.S. Pat. No. 4,983,454, an acrylic resin based on 2-octyl acrylate and other (meth)acrylic monomers, prepared in an aqueous solvent, is used as barrier-forming coating interposed between, on the one hand, a metal substrate covered with a layer of paint obtained by electrode position and, on the other hand, an upper layer of paint. The acrylic resin exhibits a glass transition temperature of −52° C. and an elongation at break at −20° C. of 610%. This coating is presented as flexible, adhesive and in particular capable of absorbing energy in order to protect the composite material against impacts, this composite material advantageously constituting a motor vehicle paint.
The applicant company has now discovered that it is possible to use 2-octyl acrylate of renewable origin to prepare a copolymer exhibiting specific properties well suited to forming a binder in coating compositions, this coating having properties identical with those obtained with monomers resulting from the petrochemical industry.